Fuel injectors have a nozzle body and an injector body that are combined axially into a structural unit by means of a clamping sleeve. Depending on the specific design of the fuel injector, the injector body can be subdivided further. In the case of a pump-nozzle injector, for instance, the injector body is divided into a spring body or spring retainer and a pump body having a typically laterally projecting control valve. The spring body and pump body are likewise clamped together by the clamping sleeve. Other fuel injectors having a multi-part or single-part injector body can be found in the prior art, with the clamping sleeve clamping together the main constituents of the fuel injector. The fuel injector can be inserted into an internal combustion engine's housing, usually a cylinder head, and supplies the combustion chambers of the internal combustion engine with fuel.
Inside the fuel injector, the fuel conveyed by the fuel injector (pump-nozzle concept) or the fuel conveyed under high pressure through the fuel injector (common-rail concept) reaches the nozzle body via lines and, when a valve-needle opening pressure has been exceeded, is injected from said body into the combustion chamber of the internal combustion engine via nozzle openings.
Because the fuel can never be completely free from particulate impurities due to, for instance, burrs and dust in the cylinder head, and in order hence to protect the very small nozzle openings in the nozzle body from clogging and to prevent consequent changes in the volume of injected fuel as well as imprecise injection jet characteristics, it is necessary to filter the fuel requiring to be injected by the fuel injector and thereby eliminate or reduce the risk of clogging.
Provided therein in the prior art in the area of an annular fuel-inlet conduit to the fuel injector in a nozzle clamping nut are relatively large bores leading to a supply line that extends to the control valve inside the fuel injector. The bores in the nozzle clamping nut are therein evenly disposed around its circumference, with an annular filter set in the nozzle clamping nut having being applied in the circumferential direction around the bores.
DE 197 52 834 A1 further discloses a nozzle clamping nut that implements a filter function without an additionally applied annular filter. Provided in an inlet area on the nozzle clamping nut are a multiplicity of filter bores therein disposed evenly around the nozzle clamping nut's circumference in a plurality of rows. The diameter of the filter bores is preferably 30 to 90 μm and the filter bores are by preference embodied conically. In the case of a preferred production method using a pulsed electron or laser beam the result is further a helical row of filter bores in the circumferential direction in the circumferential wall of the nozzle clamping nut.
Because a clamping sleeve on a fuel injector is exposed to high thermal (−40° C. to 150° C.) and high mechanical loads (vibration loading due to a piezoelectric stack operating in the fuel injector), said sleeve should as far as possible have no preset breaking points so that a clamping sleeve of said kind will have an insured durability. A clamping sleeve having a circumferential wall embodied in the circumferential direction without interruptions can furthermore be constructed having a narrower width but the same strength, which requires less space inside a cylinder head. A clamping sleeve having an integral filter function furthermore poses the problem that the clamping sleeve and filter have been produced from the same material. That on the one hand necessitates a compromise in how the clamping sleeve or, as the case may be, filter is worked because the clamping sleeve is subject to different requirements in being worked from those applying to the filter provided therein. On the other hand a compromise has to be found in the choice of suitable materials as they are subject to different requirements: the filter must provide as efficient as possible a filtering function, whereas the clamping sleeve must provide an as durable and as strong as possible connection between the main components of the fuel injector. The main focus here is on the integrity of the fuel injector, meaning that compromises usually have to be made with the filter.